A knock determining apparatus of a typical internal combustion engine includes a knock sensor attached to the cylinder block of the internal combustion engine. The knock sensor detects vibration of the cylinder block caused by a knock. The determining apparatus extracts the knock frequency component from an output signal of the knock sensor by a band-pass filter every time one combustion is occurred, and compares a peak value of the knock frequency component for one combustion with a knock determination threshold value to conduct knock determination.